Display is the process of converting an electrical signal (data information) into visible light (visual information), and devices implementing display, i.e., Man-Machine Interface (MMI) and Flat Panel Display (FPD), are currently the most popular type of display devices. Liquid crystal display (LCD) is the first developed and commercialized product among FPDs. At present, Thin Film Transistor Liquid Crystal (TFT-LCD) has become the mainstream product in LCD applications.
The development of TFT-LCD has gone through a long period of basic research, and after realizing large-scale production and commercialization, the TFT-LCD products are getting larger and larger in size and more and more widely used due to the advantages of lightness, being environmentally friendly, high performance, etc. thereof. TFT-LCD applications can be found everywhere, from small-sized mobile screens to large-sized notebook PCs or monitors and large-format liquid crystal display televisions (LCDTV). The TFT-LCDs can be divided into three categories, namely, Twisted Nematic/Super Twisted Nematic (TN/STN) type, In-Plane Switching (IPS) type and Vertical Alignment (VA) type, respectively. The early commercial TFT-LCD products are mainly in a Twisted Nematic (TN) type display mode, and the largest problem thereof is that the viewing angle is not wide enough. With the increase of the size of TFT-LCD products, especially the application of TFT-LCD in the field of TVs, an In-Plane Switching (IPS) display mode with a wide viewing angle has been developed and applied. The IPS display mode was first published in a paper by an American, R. Soref, in 1974, and a German, G Baur, proposed to apply IPS as a wide viewing angle technique to TFT-LCD. In 1995, Hitachi Ltd., Japan, developed the first 13.3-inch IPS mode wide viewing angle TFT-LCD product in the world.
Compared with other types of liquid crystal displays, a liquid crystal display of a VA type has a very high contrast because in an un-energized dark state, liquid crystal molecules are arranged perpendicular to the surface of a substrate without producing any phase difference and with a very low light leakage and a very low dark state brightness, and the lower the dark state brightness, the higher the contrast; so liquid crystal displays of a VA type have a very wide range of applications in large-size displays, such as televisions. However, in pursuit of higher performance specifications, increasing the response speed, lowering the threshold voltage, increasing the voltage holding ratio, decreasing the ion density and improving the display yield have become the goals pursued by various device manufacturers.